Blueberry Plants – Cooling Requirements for Blueberry Production


After the blueberry harvest, the blueberry bushes begin to develop fruit buds in the coming seasons. Then they begin to prepare for the cold winter. If cold conditions don’t hit suddenly, your pants will go into torpor and with little to worry about. All varieties of blueberries require approximately a certain number of hours of cooling. Blueberry plants need temperatures above freezing but below 45 F to meet their cooling requirements. In the fall, the temperatures will be cool enough that the plants can begin to accumulate the necessary chilling hours. The blueberry plant will not produce fruit next season if the need for cooling is not met. Extended periods of subzero weather simply delay the end of idle, but do not increase cooling requirements. Once the cooling needs of the plants have been met, the plants will begin to grow when the conditions for growth are right. It is for this reason that blueberry plants can be grown indoors due to their need for cold hours.

Cooling hours requirements

Everyone who is interested in growing their own fruit will eventually face the problem of cooling units (CU). This is especially the case when growing blueberry plants in the south. Chill hours are the cumulative hours in which temperatures range from 32 degrees F to 45 degrees F. Some other fruits such as peaches and apples that have evolved in colder climates have cold requirements.

The amount of cool temperature that the plant needs to continue its normal growth in the spring after the winter season is generally referred to as the plant’s cooling requirement. Different blueberry plants vary widely in their requirements. Blueberry growers should consider the cooling requirements of blueberry plants when selecting them for planting.

Cooling time is the amount of cold temperature required to meet the cooling time required by a blueberry plant and determine the area in which they can be planted. Temperatures between about 35 and 45 degrees F provide most of the cooling blueberry plants need. The most effective cooling temperature is 45 degrees F. Temperatures below 32 degrees F add little or nothing to the cooling needs of the plant.

Depending on the variety, blueberry plants need between 150 and 2000 hours of exposure to temperatures of 35 [degrees] F up to 45 [degrees] F are necessary to meet the cooling requirements of plants and for the resumption of growth and budding in the spring. Cooling time does not accumulate at subzero temperatures. This means that freezing temperatures do not count towards the required chill hours.

Chilling requirements for some southern blueberries.

Southern highbush varieties are blueberry plants that grow from zones 6 to 10. They require much less chilling hours than other varieties. Some need only 150 to 200 hours of chilling to produce fruit. This means that you can grow blueberries in the southern United States.

Some southern blueberry bush varieties and their cooling requirements are listed below in increasing order of cooling times.

Sun blue 150 hours of cooling

Jewel 200 hour cooling time requirement

Sharpblue 200 hour cooling time requirement

MISTY 250 hour cooling time requirement

Emerald 250 hour chill requirement This is a great option for warmer areas, because Southern Highbush plants only require 250 chill hours to produce record quantities of very large blueberries.

O’Neal 400 hours Cooling time requirement

Anniversary 500 cooling time requirements

Ozarkblue 800 hour cooling time requirement

From Southern Highbush, as seen from the list above, Sunshine Blue Blueberry plants are the least demanding in terms of cooling requirements. You need a minimum of 150 hours of cold to grow one.

Sunshine Blue has many good features. Sunshine Blue is a semi-dwarf, with pretty, deep pink flowers that turn white in spring. Produces large harvests of delicious blueberries. It can tolerate higher pH soils better than many other blueberries and is self-pollinating. The 150 hour chill requirement is less than any other blueberry plant, making it suitable for southern climates, but it is also surprisingly cold hardy and is a great addition to gardens and patios all the way to Chicago.

Rabbiteye varieties

Rabbiteye blueberries are native to the southern United States. They have been grown commercially for over 100 years and better varieties have been developed in recent years. The Tifblue Blueberry shrub was a breakthrough in hybridizing rabbiteye blueberry plants. Hybrid rabbit eye cultivars started the boom in the remarkable commercial trade in rabbit eye blueberries. This has resulted in remarkable agricultural growth in blueberry production that is reshaping the South’s economy. Rabbit eye blueberries have a cooling hour requirement of 350 to 700 hours. Rabbit eyes flower earlier but mature later than southern varieties. The shelf life of harvested rabbit eye blueberries is outstanding and generally better than tall blueberries.

Some of the popular varieties of rabbiteye blueberry bushes and their cooling requirements listed in order of increasing times for cooling are listed below.

BRIGHTWELL. 350-400 cold hour requirement.

Climax – Requirement of 450 to 500 hours of cold.

FIRST 550 cold hour requirement.

TIFBLUE 550-600 cold hour requirement.

PALE BLUE 550-650 cold hour requirement.

Northern varieties

The tall shrub varieties of the north require a large number (usually 800 to 1000) of chill hours to produce blueberries. These blueberry plants grow in zone 3 to zone 7.

If a blueberry bush doesn’t get the required amount of chill hours, it can grow well, and will often grow, but it won’t produce blueberries.


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